Dissolution Behavior and Varied Mesoporosity of Zeolites by NH4F Etching. Issue 16 (25th February 2022) - Qin, Zhengxing
Abstract: The mesopores formation in zeolite crystals has long been considered to occur through the stochastic hydrolysis and removal of framework atoms. Here, we investigate the NH4 F etching of representative small, medium, and large pore zeolites and show that the zeolite dissolution behavior, therefore the mesopore formation probability, is dominated by zeolite architecture at both nano‐ and sub‐nano scales. At the nano‐scale, the hidden mosaics of zeolite structure predetermine the spatio‐temporal dissolution of the framework, hence the size, shape, location, and orientation of the mesopores. At the sub‐nano scale, the intrinsic micropore size and connectivity jointly determine the diffusivity of reactant and dissolved products. As a result, the dissolution propensity varies from removing small framework fragments to consuming nanodomains and up to full digestion of the outmost part of zeolite crystals. The new knowledge will lead to new understanding of zeolite dissolution behavior and new adapted strategies for tailoring hierarchical zeolites. Abstract : Based on the particularities of zeolites dissolution topology, hidden mosaic structures and zeolite microporosity are identified as interlocking factors in shaping the final dissolution behavior of zeolites and the resultant mesoporosity pattern. The size, shape, concentration, and spatial distribution of the mosaic structures predefine the size and morphology of the void space left by dissolution. The dimensions and topology of the micropores determine the dissolution preference towards single framework atoms, interior mosaic blocks, or exterior features of zeolite crystals.